Turbine discharge temperature control system



J. H. BAKER 2,938,331

TURBTNE DISCHARGE TEMPERATURE CONTROL SYSTEM May 31, 1960 Filed Dec. k721, 1953 TURBINE DISCHARGE TEMPERATURE CONTROL SYSTEM John H. Baker, Washington, D.C., assigner to the United States of America as represented by the Secretary of the Air Force Filed Dec. 21, 1953, Ser. No. 399,646

2 Claims. (Cl. 603`S.6)

This invention relates to a system and apparatus for automatically regulating the turbine gas temperature in a turbo-jet engine. This invention is particularly applicable and presents a satisfactory solution to a problem of long standing in turbo-jet engines of advanced design, particularly those employing exhaust reheat apparatus for thrust augmentation.

Itis well known in the engine art to employ a variable area jet nozzle on a turbo-jet engine to increase the engine etnciency and control its output. Systems and devices have been previously employed to attempt to provide positive control of the variable area jet nozzle where an exhaust reheat system is employed but each has been deficient in presenting a proper solution to the problem in that the systems have had time lag and delayed action response to requirements for regulation of the nozzle area particularly where transients are involved.

To properly provide an understanding of the invention, the problem solved must be understood. Where an exhaust reheat cycle is employed in a turbo-jet engine, fuel is injected downstream of the turbine and burned in the tailpipe of the engine yielding a nozzle discharge gas temperature which may approach the range of 3000 F. with a resulting high velocity of discharge through the jet nozzle. This can produce a net thrust increase or thrust augmentation up to 45% at take oit and at least 90% in high speed tlight. It is noted that this additional thrust is obtained at the expense of specific fuel consumption but proportionately little weight is added to the propulsion unit. However, this turbine discharge temperature if not properly regulated to a temperature safe for the turbine will seriously affect the turbine wheel in the following manner. Though the temperature of the tailpipe burning ame cannot atfect the turbine wheel directly, there is a considerable indirect effect since the beginning of tailpipe burning is immediately accompanied by a rise in turbine discharge static pressure proportional to the amount of reheat fuel being burned. This produces a decrease in pressure drop across the turbine and a decrease in its speed. This would result in an increase in main system fuel flow to restore speed causing an increase in fuel-air ratio and an increase in the temperature of the gas passing through the turbine. Where the temperatures become injuriously high as can be readily seen there is damage and a resulting loss of etliciency and output.

Thus to meet the problem while the invention utilizes a variable area jet discharge nozzle, a novel control systern and apparatus is employed to accomplish the turbine discharge temperature control through variation of the variable area jet nozzle. This novel system is quick, accurate and eicient in response to conditions indicating a need for temperature regulation in the engine and utilizes turbine discharge static pressure as a controlling parameter.

Means for providing temperature control which are directly responsive to temperature are satisfactory control means where steady or slow changing conditions exist in the engine. But where transients resulting from medium to fast throttle advances appear the temperature responsive control means lag and are subject to delayed action response providing inadequate regulation of the turbine discharge temperature. Accordingly a pressure control unit is utilized in conjunction with a temperature responsive unit in the system and apparatus of the invention to substitute a static discharge pressure control signal where transients appear for the temperature responsive control signal, since the static discharge pressure anticipates the temperature change in the turbine and provides immediate regulation of the variable area jet nozzle to prevent injuriously high discharge temperatures. As can be readily seen this provides quick accurate and etlicient control of turbine discharge temperature at all times.

An object of this invention is to provide a new and novel control system and apparatus for regulating the turbine discharge temperature in a turbo-jet engine.

Another object of the invention is to provide an irnproved and novel control system for a variable area jet nozzle in a turbo-jet engine whereby engine efiiciency can be controlled with a high degree of accuracy.

A further object of the invention is to provide a novel control system and apparatus for controlling turbine discharge temperature in a turbo-jet engine employing exhaust reheat apparatus.

Other objects and advantages of the invention will be readily apparent to one versed in the art from the following description and accompanying drawing wherein:

The figure shows diagrammatically the system and apparatus of the invention.

As can be seen in the drawing the system is related to a turbo-jet engine 1 and is associated with the tailpipe section 2 thereof on the discharge side of the turbine (not shown). The exhaust reheat apparatus of the engine may comprise as shown, a set of fuel injector nozzles 3 connected to a fuel supply pump 4 and having a ow regulating means 5 of a suitable nature which is controllable by a reheat throttle 6. In the system shown in the drawing the reheat fuel pressure or flow may be given altitude compensation alone by means of an ambient pressure input as indicated or where both altitude and air speed compensation are desired, this may be accomplished by means of ram pressure input. It is noted that fuel is also metered as shown to a pilot burner 7 adjacent the fuel discharge nozzles. In actual practice a main fuel throttle would also serve the function of the reheat throttle.

Connected in the tailpipe 2 is a turbine static discharge pressure pick off line 8. The line 8 is directly connected to a bellows member B1 and to a bellows member B2 by a conduit 9 having a capillary restrictor tube section 9a therein and a solenoid valve 10 which is normally open and controllable by relay contacts Ra. The contacts Ra are part of a relay having a coil R1 and additional relay contacts'Rb, Rc, Rd, and Re. When relay coil R1 is energized, it reverses the conditions of contacts Rb to Re. The conduit 9 has a pressure reservoir 12 connected therewith. The intake ends of the bellows members B1 and B2 are fixed and the other ends thereof are relatively movable and each connected respectively to rods or bars 13 and 13. The members 13 and 13 extend through a xed guide plate 14. Spring elements 15 and 15 are interposed between the respective bellows and the plate 14 to provide a predetermined bias resisting expansion of the bellows members. Potentiometers P1 and P2 are respectively geared to the rod or bar members 13 and 13. Center taps are taken oit the respective potentiometers to an A.C. amplilier 16. The relay coil R1 and associated relay contacts Rb and Rc are interposed between the potentiometers and the A.C. amplifier. A source of power, of course, is directed to the potentiometers.

Following the turbine section in the engine 1 is a thermocouple unit 17 arranged to sense the turbine discharge temperature. Asignal of a variation Ain turbinev discharge temperature from a predetermined range is transmitted, as shown diagrammatically, by a temperature reference unit 18 of a suitable nature through a converter and normally closed relay contacts Rb and Re tothe A.C. amplifier 16. The output from the amplifier 16 is directed to a dscriminator 19 which determines the phase of the signal and transmits it to a power ampliier 20 and the appropriate contactors C1 or C2 to a reversible motor M which is the control unit for an actuating unit 21 which maybe mechanical in nature or otherwise, as desired. The actuating unit 21 controls the variable area'jet nozzle In4 application of the'system and apparatus of the invention, a continuous temperature sensing signal of turbine discharge temperature is transmitted by the thermocouple unit 17. This unit provides 'direct sensing and where there are changing conditions a signal is transmitted throughthe A.C. amplilier 16 to control the jet nozzle discharge area. The direct temperature sensing unit is only veffective to transmit a signal where there are steady or slow changing conditions. Upon a quick and rapid change in conditions in the discharge of the engine, thedirect temperature sensing unit is not effective and the invention employs a synthesized signal to anticipate turbine discharge temperature and provide immediate engine control. Where there is a transient the turbine discharge static pressure pick oi line 8 transmits the pressure indication in the tailpipe 2 directly to bellows B1 and in delayed fashion through the capillary restrictor section 9a and normally open solenoid valve 10 to bellows B2. Naturally where the pressure change is rapid resulting from a transient condition a pressure differential quickly occurs between bellows B1 and B2. This differential is evidenced electrically by the corresponding potentiometers P1 and P2 and on reaching a predetermined, critical Value the relay coil R1 is energized to close relay contacts Ra, Rb, and Rc and to open relay contacts Rd and Re. Closure of Ra completes the circuit of a solenoid S to cause valve 10 to shut. This freezes bellows B2 and potentiometer P2 at the displacement reached just before the relay coil R1 was energized. In other words, the shutting of valve 10 blocks equalization of pressure on bellows B1 and B2 and thus freezes the diierential pressure between them to at least the critical value until the servo-operated flaps 22 readjust the jet nozzle flowarea to correct this temperature-controlling parameter in a sense opposing the condition which produced the sudden pressure change sensed by the unit including bellows B1 and B2 and associated elements. For example, assume the pressure in tail pipe 2 rises rapidly. When this rise reaches a critical value, bellows B1 will be displaced rapidly to a critical extent in excess of the time-delayed displacement of bellows B2. Valve 10 will shut, preventing dissipation of the differential pressure between the two bellows. Since the pressure on bellows B1 is on the rise, the diderential pressure between the bellows and bellows B11 likely increases until' the conditions producing the pressure rise are corrected by adjustment of a temperature-controlling parameter such as the jet nozzle flow area. Simultaneously with closure of relay contacts Ra, the relay contacts Rb and Rc were closed and the relay contacts Rd and Re were opened. Thus, the synthesized temperature sensing signal from the pressure change unit is substituted for the direct temperature sensing signal to control the discharge area of the jet nozzle under rapidly changing conditions. The phase of the control signal will determine whether the jet nozzle discharge area is increased or decreased. A rising pressure increases the area and vice versa. Accordingly where there is a fast change in turbine discharge static pressure the pressure change sensing unit takes over, anticipating conditions resulting in a change in turbine discharge temperature. For example, if a sudden pressure rise is sensed by the pressure change sensing unit, this unit acts rapidly, in place of the direct temperature sensing unit,

to cause the nozzle area to increase. This lowers the turbine discharge pressure, and when the pressure on B1 approaches that of B2, the voltage diierence between the center taps of P1 and P2 approaches zero. Relay coil R1 and contacts Ra to Re operated by the coil return to normal and the jet nozzle area is then back on true, direct temperature control. If any small temperature error remains, it will be eliminated by appropriate nozzle area adjustment initiated by the direct temperature sensing circuit. Y

Accordingly, since a rise in turbine discharge static pressure occurs simultaneously with an increase in reheat burning and an increase in turbine discharge temperature can be readily anticipated and vice versa, the turbine discharge static pressure provides an immediate synthesized temperature sensing' signal anticipatory of the turbine discharge temperature. It is obvious that a null seeking control system which is operated by changes in turbine discharge static pressure will initiate nozzle changes much sooner than if an actual temperature signal were the input to the jet nozzle control. This would be true even if the temperature sensing device were to have a zero time constant as the time delay constants of the turbo and the delay of fuel supply from its main fuel system would act to delay the temperature signal.

The anticipatory nature of the synthetic temperature signal from the pressure change unit providing immediate control of the jet nozzle area to increase or decrease the turbine discharge static pressure will reduce to a considerable extent the temperature overshoots inherent in a transient control system based on actual gas temperature.

The advantages of the novel control system described will be readily apparent to those versed in the art and many variations and modifications of the invention as presented would involve mere design and are within the scope of the invention` What is claimed is:

1. A control system for automatic regulation of turbine discharge temperature in an engine having a variable area discharge nozzle comprising a temperature sensing unit, means transmitting a signal from the temperature sensing unit upon normal variation of turbine discharge temperature from a predetermined range comprising a temperature reference unit in circuit with said temperature sensing unit, a converter in circuit with said temperature reference unit, a pair of normally closed relay contacts and an alternating current amplifier in circuit therewith, a turbine discharge static pressure sensing unit responsive to rapid changes in turbine discharge' static pressure to transmit an appropriate signal, said alternating current amplifier normally operatively connected to said temperature sensing unit and normally disconnected from said static pressure sensing means, pressure responsive means in engagement with said static pressure sensing unit, relay coil means controlled by said pressure responsive means, and a second pair of normally open relay contacts in circuit between said relay coil means and said alternating current amplifier operative on a predetermined rapidity in change of turbine discharge static pressure to disconnect the temperature sensing unit signal means and connect the static pressure sensing means for transmission of a signal through said amplifier to the variable area nozzle whereby turbine discharge temperature may be controlled.

2. A control system for automatic regulation of turbine discharge temperature in a turbo-jet engine employing an exhaust reheat system comprising in combination a temperature sensing unit arranged in the turbine discharge, a turbine discharge static pressure sensing unit connected in the engine following the exhaust reheat apparatus 5 f: comprising a static pressure line attached to the engine, a first and a second bellows assembly connected, respectively, directly and indirectly to said static pressure line -and a potentiometer attached to and under diierential pressure control of said bellows assembly responsive to a rapid change in turbine discharge static pressure, alternating current amplifying means operatively connected normally with the temperature sensing unit to receive a signal therefrom, means responsive to the sensing of a predetermined rapidity of change of turbine discharge static pressure by the static pressure sensing unit operative to substitute a signal from the static pressure sensing unit for the signal from the temperature sensing unit, and relay contact means operatively connected to said alternating current amplifying means to regulate said change, l5 2,762,194

whereby the turbine discharge temperature may be controlled.

References Cited in the le of this patent UNITED STATES PATENTS 2,641,105 Drake June 9, 1953 2,662,372 Oiner Dec. 15, 1953 2,671,620 Andrews Mar. 9, 1954 2,674,843 Lombard Apr. 13, 1954 2,677,233 Jordan May 4, 1954 2,714,801 Sarles Aug. 9, 1955 v2,726,507 Baker et al Dec. 13, 1955 2,738,644 Alford Mar. 20, 1956 2,760,337 Ciscel et al. Aug. 28, 1956 Kunz et a1 Sept. 11, 1956 

